The currently available lunch bags or cooler bags are made with a liner, which is fixed and is not waterproof. When there is a spill inside of it, much of the bag can be stained and soiled and then the bag can not be cleaned thoroughly, because it is impossible to clean the layer between the liner and the exterior of the bag. If the liner is damaged, it can not be replaced and the bag is rendered useless. Because of the fact that lunch bags get dirty easily and can not be cleaned well and that the fixed liner can not be replaced once it is broken, lunch bags are deemed disposable items. For these reasons, lunch bags are made with cheap material and shoddy craftsmanship. Some lunch bags are made with fashionable designs and appear artistic, but it is a pity that unfortunately they are discarded sooner or later after they become too dirty to use. Because of the fixed liner, the cooler bags and lunch bags are only dedicated to their intended use and can not be applied to other usage.
I have designed a cooler bag/lunch bag with a detachable liner, which confers a dual use both as a cooler/lunch bag and a usual carry/shopping bag. When the liner is detached and folded up on the bottom of the bag, the cooler/lunch bag is converted to a carry/shopping bag. The liner can be made in different shape to fit in bags of different shapes.
The detachable liner is made of a complete piece of plastic, silicone or rubber is thus waterproof. The liner can be removed, cleaned or repaired and the cooler/lunch bag can be machine-washed too. The liner can be replaced whenever it is damaged. This design allows the cooler/lunch bags to be maintained in good condition easily and makes the long-term use possible. Therefore, better materials, designs and craftsmanship are worthwhile for such cooler/lunch bags.